The heart is a series of pumps that are carefully controlled by a very special electrical system. This electrical system attempts to regulate the heart rate between 60 and 150 beats per minute. With normal conduction, the cardiac contractions are very organized and timed so that the top chambers (the atria) contract before the lower chambers and the heart rate is maintained between 60 and 150 beats per minute.
Abnormally fast heart rates, called tachycardias, occur when the ventricular chambers beat too quickly. In such an instance, the ventricles may not be able to fill with enough blood to supply the body with the oxygen rich blood that it needs. Conventionally, ventricular tachycardia (“VT”) has been controlled by medication and electrical methods. The most common conventional electrical therapy for VT is implantation of a device known as an Implantable Cardioverter Defibrillator or ICD.
The conventional ICD applies an electric shock to the heart muscle to interrupt or disrupt the fast rhythm. The electric shock may be in the form of specially timed pacemaker pulses (unfelt by the patient), called antitachycardia pacing, and/or by high voltage shock. The high voltage shock, if required, is usually felt by the patient.
Cardiac pacers, which provide stimulation to a patient's heart, by means of amplitude and frequency modulated electrical pulses, have been developed for permanent or temporary applications. The two most common types of cardiac pacers currently in use are pacemakers and implantable cardioverter-defibrillators (ICD). Cardiac pacers can be implanted in a suitable location inside the patient's body or located outside the patient's body.
The human heart may suffer from two classes of rhythmic disorders or arrhythmias: bradycardia and tachyarrhythmia. Bradycardia occurs when the heart beats too slowly, and may be treated by a common implantable pacemaker delivering low voltage (about 3 V) pacing pulses.
The conventional implantable pacemaker is usually contained within a hermetically sealed enclosure, in order to protect the operational components of the device from the harsh environment of the body, as well as to protect the body from the device. This implantable pacemaker operates in conjunction with one or more electrically conductive leads, adapted to conduct electrical stimulating pulses to sites within the patient's heart, and to communicate sensed signals from those sites back to the implanted device.
Furthermore, the conventional implantable pacemaker typically has a metal case and a connector block mounted to the metal case that includes receptacles for leads which may be used for electrical stimulation or which may be used for sensing of physiological signals. The battery and the circuitry associated with the common implantable pacemaker are hermetically sealed within the case. Electrical interfaces are employed to connect the leads outside the metal case with the medical device circuitry and the battery inside the metal case.
Electrical interfaces serve the purpose of providing an electrical circuit path extending from the interior of a hermetically sealed metal case to an external point outside the case while maintaining the hermetic seal of the case. A conductive path is provided through the interface by a conductive pin that is electrically insulated from the case itself.
Such interfaces typically include a ferrule that permits attachment of the interface to the case, the conductive pin, and a hermetic glass or ceramic seal that supports the pin within the ferrule and isolates the pin from the metal case.
In all of the conventional electrical stimulus devices, the conventional ICD senses a fibrillation or tachycardia cardiac state and proceeds to use various measures to bring the heart out of the fibrillation or tachycardia, through defibrillation by antitachycardia pacing, and/or by high voltage shock. In other words, the heart has already reached a dangerous state before the conventional ICDs provide any stimulus to rectify the problem.
Therefore, it is desirable to have a device that can sense or detect an approaching fibrillation or tachycardia cardiac state and take remedial actions prior to the heart entering a dangerous state. Moreover, it is desirable to have a device that can sense or detect a failure of remedial actions and provide, as a backup remedy, the conventional defibrillation by antitachycardia pacing, and/or by high voltage shock.